The present invention relates to a decoding apparatus for decoding encoded video and audio data, and particularly relates to copyright protection technology.
The amount of information in digitized video and audio data is usually reduced by high-efficiency coding process and then the resultant data is multiplexed so as to be recorded on a recording medium or transmitted. The major examples of the recording medium include a DVD (Digital Versatile Disc). The major examples of the transmission include distribution via a digital television broadcast or the Internet.
Video data is encoded mainly according to the MPEG-2 (Moving Picture Experts Group-2) standard, the MPEG-4 standard, or the like, while audio data is encoded mainly in accordance with Dolby Digital, DTS (Digital Theater Systems), MPEG Audio, PCM (Pulse Code Modulation), or the like.
Audio data encoded according to these encoding methods will be hereinafter referred to as “encoded audio data”. In many cases, multiple channels of audio data are encoded as encoded audio data.
If video and audio are converted into digital data, they can be recorded or transmitted more conveniently, while replication thereof without degradation becomes possible, leading to the problem of copyright infringement. In order to deal with this problem, a technique for embedding copyright information in video and audio data has been developed. Although detailed explanation of this technique will be omitted herein, this kind of technique has already been employed in DVD-Audio and the like, for example.
To detect copyright information, it is required to decode video and audio data and to perform detection process. Another method is to manage copyright information by carrying out communications with a network and the like. For example, Japanese Laid-Open Publication No. 2002-359835 discloses an example of a technique in which a database for authentication is used.
Also, an external device, such as an AV (audiovisual) amplifier, can be connected to systems for playing back CDs (Compact Discs) and DVDs. For instance, audio data encoded by an encoding method, which cannot be played back by a DVD player, can be played back by an AV amplifier connected to the player.
However, it requires a complicated procedure to perform authentication with respect to packaged media, such as CDs and DVDs, by way of a network. In addition, systems with network function can only play back such data.
Furthermore, when data is played back by a connected external device, a problem arises in that the DVD player cannot check copyright information in encoded audio data output to the external device.